1. Field of the Invention
The present invention relates to a method for applying electromagnetic wave and ultrasonic wave therapies.
2. Related Art Statement
A fresh cut piece of an animal tissue or a material for simulating a living tissue made of, for example, KONNYAKU (devil's tongue), gelatin (jelly), agar, rubber or starch paste, has been proposed to prepare a phantom (a model for stimulating a living tissue) used in the practice of electromagnetic wave therapy (thermal therapy), radiotherapy or ultrasonic wave therapy. Although some of these known materials have been used practically, they have many problems.
A phantom simulating a living tissue is required for the therapy, in which electromagnetic waves or ultrasonic waves are used, for the following reasons.
When a lesion site is irradiated with a radioactive ray, the normal or healthy tissue present between the source of radioactive ray and the lesion site cannot be neglected. If the living tissue interposed between the source of radioactive ray and the lesion site is flat and has an uniform thickness, the attenuation of the radioactive ray by the interposed tissue can be estimated to control the radioactive ray so that the lesion site is irradiated with a desired dosage of radioactive ray. However, since the surface of the patient body is generally not flat and even, the interposed tissue cannot be closely estimated as an equivalent attenuating region (a flat plate-like region having a uniform thickness) to pose a problem for execution of radiotherapy. In order to overcome the problem, it has been tried to flatten the body surface or the surface of the interposed tissue. Although a method of compressing the body surface to deform the vicinity of the body surface has been adopted as a tentative measure, the deformation of the body surface tissue (flattening of the body without invading the tissue) is limited and only a limited effect is obtained by such a measure. Accordingly, it is a common practice to apply a material for simulating the living tissue on the surface of the body or skin, followed by molding the living tissue simulating material to have desired shape and dimensions to provide a flat surface which is normal to the direction from the lesion site to the source of the ray. Thus, there is a demand for a material which can simulate a living tissue and moldable to have a desired shape to be closely fitted on the surface of the patient's body and which exhibits a radioactive ray attenuation equivalent to that of the living tissue.
It is also desired that the material has characteristics under the irradiation of a radioactive ray similar to those of the living tissue in order that a model for examining the details of the attenuation of the radioactive ray in the living body. In the ultrasonic wave therapy (thermal therapy), a major portion of the ultrasonic waves is reflected by a small amount of air bubbles present between the surface of the skin and a probe or terminal for discharging ultrasonic waves when the probe or terminal contacts the surface of the patient's body. In order to eliminate such a disadvantageous effect, a material for removing air is interposed between the probe and the surface of the skin. Therefore, there is a demand for a material which can be applied closely to both of the probe and the surface of the skin and has ultrasonic properties (impedance) equivalent to that of the living tissue.
The temperature of the lesion site internally of the patient's body irradiated with an ultrasonic wave, radio wave or microwave must be maintained at a temperature of from 41.5.degree. C. to 43.degree. C. for a predetermined time when thermal therapy is applied for the medical treatment of cancer. Prior to the practical medical treatment, it is essential to learn the temperature rise in the internal sites in the patient's body under varying irradiation conditions (frequency, duration of irradiation, etc.). For such purpose, a material having thermal characteristics equivalent to those of the living tissues is demanded to prepare a model for simulating the living body.
It will be seen from the foregoing that there has been a demand for a material for simulating a living tissue to be used in medical treatment in which an ultrasonic wave or an electromagnetic wave is used. One example of the materials for simulating a living tissue is a fresh tissue of a killed animal extracted immediately after killing. However, it is difficult to have such a fresh animal tissue at every moment when it is demanded, and the electromagnetic and ultrasonic properties of the fresh animal tissue are abruptly changed even if such an animal tissue is stored in a cold place (H. F. Bowman, "Ann. Rev. Biophys. Bioeng.", 4, 43 (1975); F. K. Storm et al, "Int. J. Radiation Oncology Biol. Phys.", 8, 865 (1982); and R. V. Damadian, U.S. Pat. No. 3,789,832 (1974)). Accordingly, searching works for natural or artificial materials for simulating living tissues have been continued.
Since the living tissues generally have the electromagnetic and ultrasonic properties resembling those of water, it has been proposed to use water or a hydrogel having a high water content is used as a material for simulating a living tissue. For instance, a water bag (a pouch containing water) is placed on the surface of the skin for flattening the irradiated surface in the radiotherapy and a water bag is also placed on the surface of the skin for excluding the disturbance by air (for preventing reflection or diffusion and for matching the impedances) in the thermal therapy in which an electromagnetic wave or an ultrasonic wave is used (U.S. Pat. No. 2,789,557). However, it is difficult to achieve stable operation by the use of a water bag due to deformation and dislocation of the bag. In order to avoid such disadvantages, the use of a high water content hydrogel, such as jelly, KONNYAKU or agar, has been proposed. Since they contain 96 to 98% of water, they have the properties resembling those of the living tissues, and yet they have tentative shape-retaining properties. However, jelly (gelatine) is so soft and easily deformed. Agar is fragile and easily broken, and KONNYAKU is greatly deformed or shrunked due to syneresis after it is molded. In addition, these known hydrogels are too high in water content as compared with those of the living tissues (the water content of soft living tissues ranges from 70 wt% to 80 wt%), and thus they are unsatisfactory in this respect. In order to prepare a material having properties closer to those of the living tissues, it has been proposed to replace a portion of water contained in the known hydrogel by n-propyl alcohol, glycerine, polyethylene glycol, sodium carbonate or graphite powders. However, the qualities of the materials from natural resources, such as agar and KONNYAKU, are unstable so that it is difficult to supply stable standardized products.
With the aim of preventing deformation of the aforementioned gelatine product, it has been tried to cross-link gelatin by formalin or glutaraldehyde. (E. L. Madsen et al, "Ultrasound in Med. Biol.", 8, (4) 381 (1982); E. L. Madsen et al, "Mag. Res. Imag." 1, 135 (1982); and E. L. Madsen et al, "Am. Assoc. Phys. Med.", 5, 391 (1978)). However, it was difficult to prepare a molded product of standardized quality due to uneven gelation or uneven cross-linking. High water content hydrogels prepared from polysaccharides, such as carrageenan or alginic acid, are inferior in mechanical strength similarly to agar.
Although polyacrylamide, one of the well known synthetic materials from which a high water content hydrogel may be prepared, has an advantage that a hydrogel having a controlled water content equivalent to those of the living tissues (70 to 85%) can be prepared therefrom, it is difficult to prepare a molded product of uniform quality therefrom due to difficulty in uniform gelation. The polyacrylamide gel has a further disadvantage that it is fragile and apt to be broken during the handling by pincettes. U.S. Pat. No. 2,814,298 discloses a pad made of butyl rubber loaded with titanium dioxide which is interposed between a vibrator and a surface of a human body when applying ultrasonic wave, to thereby reduce energy loss due to reflection from the surface of the body. By the use of the pad, reflection loss is somehow improved. However, energy is greatly lost when passing through the pad is that such a pad is not preferred.
U.S. Pat. No. 2,242,886 discloses a condenser electrode for use in short-wave and ultra-short wave therapy comprising an electrode plate and a paraffin block attached thereto. However, paraffin has small specific gravity and excessively low acoustic impedance, thereby causing reflection loss at the interface.
Since it is difficult to prepare a material for simulating the living tissues by the use of a water bag or a natural or synthetic gel, it is a common practice to dip the diseased site in water. For example, when mammary cancer is irradiated with an ultrasonic wave, the patient is laid in the prone posture and the downwardly extending mamma is dipped in a water reservoir to ensure removal of air bubbles from the vicinity of the surface of mamma prior to exposure to the ultrasonic wave. Although it is possible to dip mamma, the limbs, the abdominal region, the chest and the neck, a large water reservoir is required to pose inconvenience in practical operation. The face, head, eye and other internal organs cannot be treated in such condition that they are dipped in water.